1. Field of the Invention
The present invention relates to a process for evaluating corrosion inhibitors. More specifically, the invention relates to simultaneously performing a single test of multiple samples, wherein some of the samples are located in different fluids.
2. Description of the Related Art
Corrosion is the destructive attack of a material by reaction with its environment. The serious consequences of the corrosion process have become a significant problem in various environments, including manufacturing, hydrocarbon refining, drilling for minerals, and maritime operations. Corrosion causes plant shutdowns, wasted resources, loss or contamination of product, reduction in efficiency, costly maintenance, and expensive over-design of components. Furthermore, corroded components can cause unsafe conditions.
Corrosion has a tremendous impact on equipment in refineries, drilling operations, storage facilities, chemical plants, and any other facility that handles corrosive materials. A corrosive material is a fluid containing one or more corrosive chemicals. Thus exposure to the corrosive material can cause corrosion. The effects of corrosion can be reduced by adding a corrosion inhibitor to a process stream or storage unit. The effectiveness of corrosion inhibitors can change, however, depending on the physical state of the process stream and the corrosion inhibitor. During processing, liquids such as oil and water can contain corrosive materials and can separate to form stratified layers. Furthermore, outgasing can create a gas layer in the process stream, above the liquid portion of the process stream. Corrosion inhibitors can be added to the process stream to reduce the impact of corrosive chemicals, but a corrosion inhibitor that is effective in a liquid chemical can be less effective in water than in a hydrocarbon stream, and still less effective in gas than in liquid. It is useful to test corrosion inhibitors in various liquids and gas.
A coupon can be used to test a corrosion inhibitor. A coupon is a sample of material such as metal, and can be of the same type of metal as that used for equipment or pipe in a chemical processing facility. In a typical corrosion inhibitor test, the corrosion inhibitor is added to a corrosive material. A coupon is cleaned and submerged in the corrosive material for a period of time. The coupon is then removed from the corrosive material, cleaned, and weighed again. The change in weight is an indication of the effects of corrosion. A relatively small change in weight indicates an effective corrosion inhibitor.
The simplest method of estimating corrosion rate is the weight loss technique, wherein the weight of a coupon is weighed before and after exposure to a corrosive material. To perform the weight-loss corrosion estimation, the coupon is first cleaned and weighed to determine an initial weight of the coupon. The coupon is then exposed to the corrosive material for a predetermined period of time. After the exposure, the coupon is cleaned of all corrosive material and then re-weighed to determine a final weight of the coupon. The Weight Loss of the coupon is calculated by subtracting the final weight from the initial weight. The total metal loss can be calculated as follows:Metal Loss=Weight Loss(g)*K/Alloy Density(g/cm3)*Exposed Area(A)
The weight loss technique is a relatively slow measurement technique. It is often used as a calibration standard for devices that estimate corrosion, such as Linear Polarization and Electrical Resistance.
Corrosive materials can exist in different states and can include various liquids that can mix and separate during processing. For example, the process stream can include both oil and water, and corrosive chemicals can be present in both the oil and the water, and the oil and water can mix together during processing. Furthermore, corrosive chemicals in the oil/water mixture can evolve as gas or vapor and be present in gaseous form during processing. Outgassing is the slow release of a gas that was trapped, absorbed, adsorbed, or the like, in some material. It can also be the product of slow chemical reactions. Outgassing can also be used as a method to remove embedded gases, typically by heating or reducing of pressure. Various components used in manufacturing, refining, transporting, storing, or processing of oil or chemicals can be simultaneously exposed to corrosive chemicals in various forms. Some corrosion inhibitors can be suitable for protecting against such multiphase corrosion. Conventional corrosion testing only evaluates the effectiveness of one phase of a corrosive material at a time. Thus to test three phases of a corrosive material requires three separate tests which may inadequately simulate the distribution of corrosion inhibitor in any specific fluid or phase. Furthermore, performing separate tests may overlook the evolution of gases from a liquid, or the transfer of corrosive chemicals between oil and water phases that occurs in the process stream. Finally, it is time consuming to independently test each of several phases.
Therefore, improved methods for testing the effectiveness of multiphase corrosion inhibitors is needed. Specifically, a test that simultaneously exposes a material to several phases in a manner that simulates the interaction between phases that occurs in the process stream during actual operations is needed.